This invention relates to a control method for electronically controlling the quantity of fuel being supplied to an internal combustion engine immediately after cranking thereof, and more particularly to such a control method which is adapted to supply the engine with desired increased quantities of fuel responsive to a fuel increment gradually decreasing in value from an initial value thereof set in dependence on the engine temperature after termination of cranking of the engine, thereby to achieve smooth and stable engine operation.
Among conventional fuel quantity control methods for internal combustion engines, it has been widely known as starting fuel supply control to control the fuel quantity to an appropriate value corresponding to the cooling water temperature of the engine representative of the engine temperature at cranking of the engine so as to ensure positive and smooth starting of the engine, while it has also been known as basic fuel supply control to control the fuel quantity to a value dependent upon operating parameters of the engine such as engine rotational speed and intake pipe absolute pressure after the engine has got out of the cranking state. In this basic fuel supply control, increase of the fuel quantity is effected by the use of a fuel increasing coefficient decreasing in value as the engine cooling water temperature increases (hereinafter called "the water temperature-dependent fuel increasing coefficient KTW"), so as to achieve stable engine operation while the engine is in a cold state.
In order to obtain smooth transition from cranking operation of the engine under the above starting fuel supply control to normal operation of same under the above basic fuel supply control, it has been proposed by the assignee of the present application to set a value of an after-start fuel increasing coefficient KAST as a product of the value of the above water temperature-dependent fuel increasing coefficient KTW and a constant CAST' having a fixed value, set a fuel quantity being supplied to the engine immediately after cranking thereof on the basis of the above set value of the fuel increasing coefficient KAST, and subsequently gradually decrease the set fuel quantity to be supplied to the engine (Japanese Provisional Patent Publication No. 57-206737).
The rate of increase of the fuel supply quantity for obtaining smooth and positive startability of the engine according to the aforementioned starting fuel supply control at cranking is larger than that of the fuel supply quantity for obtaining stable engine operation according to the aforementioned basic fuel supply control. Therefore, if the fuel quantity being supplied to the engine immediately after cranking is set on the basis of the value of the coefficient KAST obtained by multiplying the value of the water temperature-dependent fuel increasing coefficient KTW by the constant CAST' having a fixed value according to the above proposed after-cranking fuel supply control method, there can occur a large difference in the resulting fuel supply quantity between at cranking and immediately after the cranking. This large difference can cause a degradation in the driveability of the engine to give an unpleasant feeling to the driver, and can even cause engine stall.